Astronomers have detected a mysterious signal 240 million light-years away from Earth, in the Perseus Cluster (top), one of the most massive objects in the universe. The unidentified signal is a "spike of intensity at a very specific wavelength of X-ray light." Scientists don't yet know the origin of the signal.

One of their theories is really interesting: It may be "produced by the decay of sterile neutrinos, a type of particle that has been proposed as a candidate for dark matter." According to Esra Bulbul, at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts:

We know that the dark matter explanation is a long shot, but the pay-off would be huge if we're right. So we're going to keep testing this interpretation and see where it takes us.

They are now working in finding confirmation of this interpretation, which would be a major breakthrough as nobody has been able to directly detect dark matter yet, even while astronomers estimate that dark matter constitutes 85 per cent of all matter in the universe. Some scientists are even suggesting that the origin may not be sterile neutrinos; instead, they say, "different types of candidate dark matter particles, such as the axion, may have been detected."

Listening to the music notes of the Perseus Cluster

To find this signal, a team lead by Bulbul went through 17 days' worth of observations of the Perseus Cluster taken over ten years with NASA's Chandra X-ray Observatory and ESA's XMM-Newton.

This cluster is a titan of the skies, one of the most massive known objects in the universe. It houses "thousands of galaxies immersed in a vast cloud of multimillion-degree gas." It's not the first time that scientists have detected cool stuff here. Back in 2003, researchers "listened" to "one of the deepest notes ever detected," one that has an oscillation period of 9.6 million years. That's "57 octaves below the keys in the middle of a piano." Here's that note, accelerated:

This video (below) shows the location of the Perseus Cluster on Earth's sky, as well as zooming into some of the galaxies contained in it.